As thin and short communication devices become popular, developers have to design communication system within limited spaces. For example, developers have to design communication system with a plurality of antennas in a small space. However, when two antennas are designed in a same small space, if isolation between the two antennas is not good enough, interference between the two antennas would be large. Thus, signals transmission is affected. Transmission rate is decreased as well. Moreover, it is easy to generate current interference at an edge of the ground when two antennas are disposed in two sides of the ground. Improvement in the art is preferred.